ADV
ANCEINFORMA
TION
TMS320F28377S, TMS320F28376S, TMS320F28375S, TMS320F28374S
SPRS881A – AUGUST 2014 – REVISED JUNE 2015
5.7.3.4
Crystal Oscillator
When using a quartz crystal, it may be necessary to include a damping resistor (R
D
) in the crystal circuit to
prevent over-driving the crystal (drive level can be found in the crystal data sheet). In higher-frequency
applications (10 MHz or greater), R
D
is generally not required. If a damping resistor is required, R
D
should
be as small as possible because the size of the resistance affects start-up time (smaller R
D
= faster start-
up time). It is recommended that the crystal manufacturer characterize the crystal with the application
board.
Table 5-14. Crystal Oscillator Parameters
MIN
MAX
UNIT
CL1, CL2
Load capacitance
12
24
pF
C0
Crystal shunt capacitance
7
pF
Table 5-15. Crystal Equivalent Series Resistance (ESR) Requirements
(1)
MAXIMUM ESR (
Ω
)
MAXIMUM ESR (
Ω
)
CRYSTAL FREQUENCY (MHz)
(CL1 = CL2 = 12 pF)
(CL1 = CL2 = 24 pF)
10
55
110
12
50
95
14
50
90
16
45
75
18
45
65
20
45
50
(1)
Crystal shunt capacitance (C0) should be less than or equal to 7 pF.
Table 5-16. Crystal Oscillator Electrical Characteristics
over recommended operating conditions (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
f = 20 MHz; ESR MAX = 50
Ω
;
Start-up time
(1)
2
ms
CL1 = CL2 = 24 pF, C0 = 7 pF
(1)
Start-up time is dependent on the crystal and tank circuit components. It is recommended that the crystal vendor characterize the
application with the chosen crystal.
Copyright © 2014–2015, Texas Instruments Incorporated
Specifications
65
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